This invention relates to a self-aligning thrust roller bearing incorporating at least two coaxial race tracks and a number of rollers provided between the race tracks and in engagement with these, said rollers being arranged in at least two rows beside each other, the race tracks and the rollers being curved in cross-section and the axes of the rollers being inclined in the same direction relative to the bearing axis.
Spherical thrust roller bearings are earlier known. These bearings generally have one row of unsymmetrical rollers, one bearing ring with a spherical race track and one bearing ring with a roller guiding flange.
Rings having flanges are expensive to manufacture and bearings having such rings have a high starting friction. It is thus desirable to avoid the need of the flange. A possible method for avoiding a flange is to use symmetrical rollers. A roller is in this respect considered to be symmetrical if it can be divided in two congruent halves with a cross sectional plane half way between the ends of the roller. Symmetrical rollers having such a large axial extension and being arranged with such a large angle between the roller axis and the bearing axis as the rollers appearing in spherical thrust bearings are however difficult to guide with a desired precision. Furthermore, the sliding in the contact points between the roller and the race track will be large, which leads to power losses and a risk for bearing failure due to the generated friction heat.
The purpose of the present invention is to provide a bearing of the type defined in the preamble, wherein a good roller guiding is obtained without a flange on one of the rings and which has low friction at start and during operation.
Due to the fact that all rollers of the bearing have the same revolution angular speed about the bearing axis only one cage for the rollers is needed, which saves space and cost. A good roller guiding can easily be obtained by the rollers being arranged to contact each other adjacent the inner race ring or by means of a guiding ring at the outer race ring. Both roller rows are subjected to load when the bearing takes up axial load, which guarantees a good guiding of all rollers. By using two rollers instead of one roller with a corresponding axial extension it is possible to halve the bearing friction losses, since the relative sliding at the contact between the roller and the race track, i.e. the relation between the sliding speed and the rolling speed, is about proportional to the length of the roller.